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The safety of lithium ion batteries is correlated closely to the mechanical property and thermal stability of separators. The polymer/ceramic particle composite separators are widely investigated for quasi-solid gel separators of lithium ion batteries, but the nonuniform dispersion of ceramic particles limits their performance. In this study, ball-milled Al-doped Li6.75La3Zr1.75Ta0.25O12 suspension is incorporated into poly (vinylidene fluoride-co-hexafluoropropylene) gel to prepare a highly uniform quasi-solid composite separator. The results show that adding only 4.29 wt% Li6.75La3Zr1.75Ta0.25O12 into PVDF-HFP increases ductility by three times and the mechanical strength by 38% as compared with pure PVDF-HFP separator. Batteries with the composite separator show significantly improved cyclic stability and rate performance at both room temperature and temperatures up to 80 °C. In particular, the composite separator promotes homogenous Li+ flux through the separator and suppresses Li dendrite growth in Li-metal based batteries.

Three-dimensional, porous graphitic carbon co-doped with cobalt and nitrogen (C-Co-N) is prepared with metal-organic framework (MOF) and employed as Lewis base matrix to host selenium. Owing to the unique structure with abundant micro/meso-pores, the highly-conductive C-Co-N matrix provides highly-efficient channels for electron transfer and ionic diffusion, and sufficient surface area for loading of selenium nanoparticles while mitigating dissolution of polyselenides and suppressing volume expansion. The homogenous distribution of cobalt nanoparticles and nitrogen-group in C-Co-N composite immobilize polyselenides through strong chemical interaction in the operation of Li-Se batteries. With a very high Se loading of 76.5 wt%, the C-Co-N/Se cathode delivers superior electrochemical performance with an ultrahigh reversible capacity of 672.3 mAh g −1 (99.6% of the theoretical value) and a capacity of 574.2 mAh g −1 after 200 cycles, giving a capacity fading of only 0.07% per cycle and a nearly 100% Columbic efficiency. In-situ Raman spectroscopy and density functional theory simulations are employed to investigate the Se (de)lithiation mechanism at the electrolyte/cathode interface, and confirm that the structure and composition of C-Co-N scaffold give rise to efficient cathode host for high-performance Se-based cathodes with dramatically reduced capacity fading.

Hierarchical structure design can greatly enhance the unique properties of primary material(s) but suffers from complicated preparation process and difficult self-assembly of materials with different dimensionalities. Here we report on the growth of single carbon tubular nanostructures with hierarchical structure ( h CTNs) through a simple method based on direct conversion of carbon dioxide. Resorting to in-situ transformation and self-assembly of carbon micro/nano-structures, the obtained h CTNs are blood-like multichannel hierarchy composed of one large channel across the h CTNs and plenty of small branches connected to each other. Due to the unique pore structure and high surface area, these h CTN-based flexible supercapacitors possess the highest areal capacitance of ∼320 mF cm −2 , as well as good rate-capability and excellent cycling stability (95% retention after 2500 cycles). It was established that this method can control the morphology, size, and density of h CTNs and effectively construct h CTNs well anchored to the various substrates. Our work unambiguously demonstrated the potential of h CTNs for large flexible supercapacitors and integrated energy management electronics.

Three-dimensional Li2S/graphene hierarchical architecture (3DLG) is synthesized with a facile infiltration method. Highly-crystalline Li2S nanoparticles are deposited homogenously into three-dimensional graphene foam (3DGF) network grown by chemical vapor deposition (CVD), resulting in 3DLG with high surface area, porosity, flexibility and conductivity. The 3DLG is employed as flexible, free-standing and binder-free cathode without metallic current collectors or conducting additives. Due to the unique structure, the 3DLG exhibits a high discharge capacity of 894.7 mAh g−1 at 0.1 C, a high capacity retention of 87.7% after 300 cycles at 0.2 C, and the high-rate capacity up to 4 C reaches 598.6 mAh g−1. The cyclic performance is record-breaking compared to the previous reports on free-standing graphene-Li2S cathodes. Flexible lithium-sulfur batteries based on the high-capacity 3DLG cathode have promising application potentials in flexible electronics, electrical vehicles, etc.

Lithium-ion batteries (LIBs) have been employed in many fields including cell phones, laptop computers, electric vehicles (EVs) and stationary energy storage wells due to their high energy density and pronounced recharge ability. However, energy and power capabilities of LIBs decrease sharply at low operation temperatures. In particular, the charge process becomes extremely sluggish at temperatures below −20 °C, which severely limits the applications of LIBs in some cold areas during winter. Extensive research has shown that the electrolyte/electrode composition and microstructure are of fundamental importance to low-temperature performances of LIBs. In this report, we review the recent findings in the role of electrolytes, anodes, and cathodes in the low temperature performances of LIBs. Our overview aims to understand comprehensively the fundamental origin of low-temperature performances of LIBs from a materials perspective and facilitates the development of high-performance lithium-ion battery materials that are operational at a large range of working temperatures.

Separator-lithium anode interface featured with uniform lithium-ion plating/stripping is of paramount importance for the safe operation of batteries. Lithium anode paired with traditional polyolefin separator is considerably challenged with uncontrolled formation of Li dendrites, giving rise to undesirable rate capacity and cycle life. In this work, through an electrophoretic deposition technique, hexafluoropropylene separator embedded with atomic interlamellar lithium-channel phyllosilicate clay is realized. With large absorption with electrolyte, the separator with interlamellar spacing of 1.31 nm provides abundant active sites for Li+ and enables fast transfer of lithium ions, giving rise to an ionic conductivity of 5.66 × 10−4 S cm−1 at ambient temperature. The parallel interlayers unify the direction of Li+ flows, which leads to the uniform deposition of Li+ on the anode and effectively eliminates lithium dendrite issues in Li+ plating/stripping processes. The cell assembled with the robust polymer/clay separator is more advantageous than state-of-the-art in the literature, delivering a reversible capacity of 152 mAh g−1 with a 98.5% capacity retention after 300 cycles at 0.5C.

In rechargeable lithium ion batteries (LIBs), the separator undergoes stresses in repeated charge and discharge processes. Polyvinylidene fluoride (PVDF) gel separators own excellent thermal stability and electrolyte wettability, but their limited mechanical strength cannot sustain severe strains under the conditions of large Li ion fluxes, mechanical and thermal shocks of batteries. In this report, a solid-electrolyte-reinforced gel separator is prepared through a single-step electrophoretic deposition on a stable surfactant-free colloid of PVDF-HFP and Al-doped Li6.75La3Zr1.75Ta0.25O12 (LLZTO). The LLZTO/PVDF-HFP separator owns a 3D laminated structure, a mechanical strength of 28.6 MPa, a room-temperature ionic conductivity of 7.13 × 10−4 S cm−1 and improved thermal stability. With the LLZTO/PVDF-HFP separator, LiFePO4 LIBs deliver a threshold discharge capacity of 170 mAh g−1 at 0.1 C and stable cycling with nearly zero capacity decay over 100 cycles at 0.5 C.

Most efforts regarding strain effect at the interfaces between electrolytes and electrodes are mainly focused on enhancing the ionic conductivity in electrolytes. However, fundamental insights into the strain effect on gas transport properties in electrodes of fuel cells are still lacking. In this report, quantitative analysis is performed to evaluate the correlation between interfacial strain and the important fuel cells parameters, including limiting current density and concentration polarization. We demonstrate that the strain effect plays an important role in the performance of solid oxide fuel cells with nanostructured electrodes. Our studies provide a powerful platform for reducing concentration polarization by engineering quantitatively the interfacial strain, and facilitating the development of high-efficiency nanostructured fuel cells.

Introducing lattice mismatch-induced tensile strain at hetero-interfaces may be an efficient approach to enhance ionic conductivity at moderate temperatures. Extensive theoretical and experimental research has focused on strain-versus-ionic conductivity correlations. However, the correlation between strain and ionic conductivity still lacks a systematic and quantitative investigation. In this report, we derive an analytical expression to evaluate quantitatively the strain-induced enhancement in ionic conductivity. We demonstrate that simulation and experimental data in the literature, are well explained in the framework of our derived expressions. Our studies provide a powerful platform for quantitatively designing and engineering heterostructure interfaces for a number of applications, including fuel cells/batteries and optical/magnetic devices.

Inefficient gas transport in the porous cathode is disastrous for the lithium–air battery to achieve a high electrochemical performance. Previous evaluation of the cathode diffusivity relies on indirect calculations based on multiple V–I data obtained over the intact battery system, which inevitably induces evaluation uncertainty and material waste. In this report, an electrochemical device is designed for the out-of-cell diffusivity measurement in the lithium–air battery with micro/nano-sized cathodes. With the measured diffusivity, a few electrochemical parameters including the limiting current density and the concentration polarization associated with the porous cathodes can thus be directly evaluated. The work facilitates the development of highly-efficient cathode materials in the general field of metal–air battery field.

Mass transport is of paramount importance to the electrochemical performance of fuel cells. The high performance of fuel cells requires a large diffusion coefficient, i.e. the diffusivity, of the gas transport in electrodes and efficient gas diffusion can lead to large limiting currents and controlled concentration polarization. Recently-designed electrochemical devices allow for the direct evaluation of gas diffusivity in fuel cells. To realize these devices, a gas pump and an oxygen sensor are typically attached to two different spots of the inside wall of an electrolyte tube, which inevitably induces the uncertainty in measurement temperature. To eliminate temperature uncertainty in the diffusivity measurement, an electrochemical device with a multifunctional sensor is designed in this report. Quantitative analysis shows that temperature uncertainty can indeed induce substantial evaluation errors of gas diffusivity, limiting current density and concentration polarization, which in turn verifies the necessity of the multifunctional sensor device for the accurate diffusivity measurement in fuel cells.

Stability is of paramount importance in organic semiconductor devices, especially in organic solar cells (OSCs). Serious degradation in air limits wide applications of these flexible, light-weight and low-cost power-generation devices. Studying the stability of organic solar cells will help us understand degradation mechanisms and further improve the stability of these devices. There are many investigations into the efficiency and stability of OSCs. The efficiency and stability of devices even of the same photoactive materials are scattered in different papers. In particular, the extrinsic degradation that mainly occurs near the interface between the organic layer and the cathode is a major stability concern. In the past few years, researchers have developed many new cathodes and cathode buffer layers, some of which have astonishingly improved the stability of OSCs. In this review article, we discuss the recent developments of these materials and summarize recent progresses in the study of the degradation/stability of OSCs, with emphasis on the extrinsic degradation/stability that is related to the intrusion of oxygen and water. The review provides detailed insight into the current status of research on the stability of OSCs and seeks to facilitate the development of highly-efficient OSCs with enhanced stability.

A reduction in Ohmic, activation and concentration-polarization losses is of paramount importance in improving the efficiency of solid oxide fuel cells, proton-exchange-membrane fuel cells, and molten-carbonate fuel cells. Efficient measurements of gas diffusivities at the operating conditions of fuel cells allow concentration polarization losses of these fuel cells to be reliably evaluated. To enhance the applicability of solid oxide fuel cells, tremendous work on the development of gas diffusion models and gas diffusivity measurement techniques have been done to pre-evaluate the concentration polarization losses of fuel cells. This review focuses on the recent advancement of gas diffusion models and diffusivity measurement techniques of solid oxide fuel cells. The review seeks to provide an insightful guidance for designing high-performance solid oxide fuel cell electrodes with efficient thickness, porosity, among other parameters.

In the previous diffusivity measurements via the electrochemical devices designed by the authors, the electronic conduction contribution of electrolyte materials was neglected, and an error in the subsequent evaluations of limiting current density and concentration polarization was consequently induced. In this report, a current-sensor and oxygen-sensor based electrochemical cell was designed for accurate diffusivity measurements in fuel cells. Our analytical investigation shows that diffusivity measurements via the new device lead to accurate analytical evaluations of limiting current density and concentration polarization in fuel cells. With the improved accuracy, one can reliably pre-evaluate the limiting current density and concentration polarization of fuel cell electrodes with different thicknesses ranging from several nanometers to a few millimeters at different operating temperatures.

To improve the efficiency of the diffusivity measurement in solid oxide fuel cells (SOFCs), a bi-sensor electrochemical cell is proposed and analyzed. The cell consists of an oxygen pump and two oxygen sensors. This bi-sensor cell doubles the efficiency of binary diffusivity measurements in both porous anodes and cathodes in SOFCs. The design provides an efficient platform to estimate the electrode limiting current density (LCD) and concentration polarization (CP) in SOFCs. Mechanism of measuring the CP with different electrode configurations was discussed in depth. The design was verified by studying the effect of electrode thickness on the CPs at different operating temperatures.

The effective binary diffusivity of H 2 and H 2 O in a Ni and yittria-stabilized zirconia (YSZ) anode of the solid oxide fuel cells (SOFCs) was measured between 650 and 800 °C using an electrochemical cell consisting of an oxygen pump, an oxygen sensor, and a porous SOFC anode pellet. The effective binary diffusivity was obtained from the relationship between the current density across the oxygen pump, and the H 2 partial pressure gradient across the anode sample measured using the oxygen sensor. The anode limiting current density and concentration polarization were estimated using the experimental results.